Disc Brake Noise

[BJMcC]

Hello, my back disc brakes are extremely noisy under heavy braking. I have searched online for solutions, and followed a few pieces of advice, however with no luck. I have checked that the disc is straight. I have ensured that the disc brake housing is securely attached to the frame. I have taken out the pads, which have plenty left on them and sanded them in case they have overheated. I have taken off the disc and cleaned it with Isopropyl alcohol and lightly sanded it, however the howl is still there. Does anyone have any advice?

[bychosis]

What brakes/bike?

[BJMcC]

The brakes are Shimano Deore XT.

[mikgit]

has it always been there? or just recently?
i had an issue years ago, put discs on my Yeti ARC, and the rear made a terrible howl and sent aweful vibrations throught the frame, was very unpleasant Couldnt figure it out spent ages fiddling with them. Turns out the seatstay was flexing/springing back like a guitar string (a horrible sounding one). Stripped the brakes off and swapped them onto my GT Zaskar,zero issues and then onto a Specialised Epic, also no issues.
Would never have picked it, but for ace bike store mechanic.

[outnabike]

I have the same on my front wheel and clean occasionally with alcohol from Bunnings.
I mean you need probably a little residue on the disc, but too much accentuates the noise. Anyway there might be better ways, but it works for me.

[Duck!]

Don't clean the rotor, it strips off the bedded-in pad material that is essential for proper brake performance. Sand the pads and leave some dust on the surface, then go and do a few good hard braking efforts, without coming to a complete stop. This will get the pad material attached to the rotor surface. Treat the brakes with some aggression when riding, using short, firm applications rather than dragging.

I'm tipping you have resin compound pads, which I have found tend to glaze and get noisy very frequently, especially if feathered. Switch to metal compound.

[djw47]

I've had this problem recently, tried everything I can think of - even tried toasting the brake pads over a gas stove to burn off any residual gunk but still the squealing comes back and the pads end up glassed over. Just ordered metal pads, fingers crossed. I'll post back here once they arrive...